Method for producing iron carbide

ABSTRACT

Provided is a method for producing iron carbide in which free carbon is generated with difficulty. When iron carbide is produced by reducing and carburizing iron-containing raw materials for iron making using a reaction gas mainly containing hydrogen and methane, steam or carbon dioxide is added into fluidized bed reactor ( 1 ) through line ( 7 ) in addition to the reaction gas supplied from line ( 2 ) into reactor ( 1 ) corresponding to a quantity of free carbon generated in reactor ( 1 ) which is obtained by means of dust meter ( 9 ). Consequently, the generation of the free carbon can be controlled.

TECHNICAL FIELD

[0001] The present invention relates to a method for producing ironcarbide (Fe₃C) suitable for raw materials for iron making or steelmaking which comprises iron carbide (Fe₃C) as a main component, forexample, raw materials for steel making which is used in an electricfurnace and the like.

BACKGROUND ART

[0002] The production of steel normally comprises the steps ofconverting iron ore into pig iron using a blast furnace, and thenconverting the pig iron into steel using an open hearth furnace or aconverter. Such a traditional method requires large amounts of energyand large-scale equipment, and has a high cost. Therefore, for asmall-scale steel making, a method comprising the steps of directlyconverting iron ore into raw materials to be used in a steel makingfurnace, and converting the raw materials into steel using an electricfurnace and the like has been used. With respect to this direct steelmaking process, a direct reduction process has been used to convert ironore into reduced iron. However, the reduced iron produced by the directreduction process is highly reactive and reacts with oxygen in the airto generate heat. Therefore, it is necessary to seal the reduced ironwith an inert gas or by some other measures during transportation andstorage of the reduced iron. Accordingly, iron carbide (Fe₃C) containinga comparatively high iron (Fe) content, and which has a low reactionactivity and can be easily transported and stored, has recently beenused as the raw materials for steel making in an electric furnace andthe like.

[0003] Furthermore, raw materials for iron making or steel makingcontaining iron carbide as a main component is not only easy to betransported and stored, but also has the advantage that carbon elementcombined with iron element can be used as a source of fuel in an ironmaking or steel making furnace, and can be used as a source to generatemicrobubbles which accelerates a reaction in the steel making furnace.Therefore, raw materials for iron making or steel making containing ironcarbide as a main component has recently attracted special interest.

[0004] According to a conventional method for producing iron carbide,iron ore fines are fed into a fluidized bed reactor or the like, and arecaused to react with a gas mixture comprising a reducing gas (e.g.,hydrogen gas) and a carburizing gas (e.g., a methane gas and the like)at a predetermined temperature. Thus, iron oxides (hematite (Fe₂O₃),magnetite (Fe₃O₄), wustite (FeO)) contained in iron ore are reduced andcarburized in a single process (which means a process performed bysimultaneously introducing a reducing gas and a carburizing gas into asingle reactor) as shown in the following reaction formula ((1), (2),(3), (4)).

3Fe₂O₃+H₂→2Fe₃O₄+H₂O  (1)

Fe₃O₄+H₂→3FeO+H₂O  (2)

FeO+H₂→Fe+H₂O  (3)

3Fe+CH₄→Fe₃C+2H₂  (4)

[0005] Furthermore, the formula (1) to (3) may be put together. As aresult, the reaction formula for deciding the progress of reduction andcarburization of iron oxide can be shown by the following reactionformula (5) and the above-mentioned reaction formula (4).

Fe₂O₃+3H₂→2Fe+3H₂O  (5)

[0006] The prior art related to the field of the present invention hasbeen described in the publication No. 6-501983 of Japanese Translationof International Patent Application (PCT/US91/05198), for example.

[0007] However, free carbon is sometimes generated depending on theproducing conditions such as a gas composition, a reaction temperatureand the like in a fluidized bed reactor. In a case where the free carbonis mixed with iron carbide, there come out the following drawbacks.

[0008] (1) There is a possibility that a dust fire or explosion might becaused by free carbon scattered in a gas exhausted from the fluidizedbed reactor.

[0009] (2) An opening such as an inlet port for raw materials, an outletport for product of the fluidized bed reactor is sometimes blocked bythe free carbon.

[0010] (3) CH₄ is consumed with the generation of the free carbon. Forthis reason, CH₄ which is necessary for the generation of iron carbideis additionally required.

[0011] (4) Once the free carbon is generated, the generation of the freecarbon is promoted.

[0012] In consideration of the above-mentioned problems of the priorart, it is an object of the present invention to provide a method forproducing iron carbide in which free carbon is generated withdifficulty.

DISCLOSURE OF THE INVENTION

[0013] In order to accomplish the above-mentioned object, the presentinvention can detect free carbon in a latter half of compartments in areactor and change a composition of a reaction gas corresponding to aquantity of the detected free carbon, thereby controlling the generationof the free carbon.

[0014] More specifically, the present invention provides a method forpreventing free carbon from being generated by thermal decompositionfrom carbon monoxide or hydrocarbon when raw materials for iron makingor steel making mainly comprising iron carbide as a main component isproduced by reducing and carburizing iron-containing raw materials foriron making mainly comprising iron oxides and iron hydroxides as maincomponents using a reaction gas mainly containing hydrogen and methane,comprising the steps of dividing an inside of a reactor into a pluralityof compartments, detecting the free carbon in a latter half of thecompartments which are closer to an outlet port for product, andchanging a composition of the reaction gas corresponding to a quantityof the detected free carbon.

[0015] As a process of detecting free carbon, it is possible to employ“a process of detecting free carbon based on a change of a temperatureof a thermometer installed in the latter half of the compartments”, “aprocess of detecting free carbon by analyzing dust picked up by a dustpick-up device installed on an upper portion in the latter half of thecompartments” or “a process of detecting free carbon based on a resultof detection of a ratio of methane to hydrogen in gas picked up by a gaspick-up device installed on an upper portion in the latter half of thecompartments”. In addition, these two or more processes can be combined.

[0016] As a process of changing the composition of the reaction gas inthe reactor, it is possible to employ “a process of increasing steam inthe reaction gas corresponding to the quantity of the detected freecarbon”, “a process of increasing carbon dioxide in the reaction gascorresponding to the quantity of the detected free carbon” or “a processof decreasing the carbon monoxide or the hydrocarbon in the reaction gascorresponding to the quantity of the detected free carbon”. In addition,these two or more processes can be combined.

[0017] The above-mentioned change of the composition of the reaction gascan be performed by controlling the composition of the reaction gas tobe introduced into the reactor.

[0018] The status of the change of iron-containing raw materials in thereactor according to the present invention having the above-mentionedconstitution will generally be described. A part of raw materials in thecompartments on the side closer to the inlet port for raw materials isconverted into Fe by mainly reducing reaction. Then, the residualreducing reaction and the carburizing reaction into iron carbide (Fe₃C)of the iron-containing raw materials are performed in the compartmentson the side closer to the outlet port for product. If the carburizingreaction in which an upper limit of a ratio of conversion into Fe₃Cobtained at a certain H₂O partial pressure is exceeded is carried out,free carbon is generated. By the following process, the free carbon isdetected. Then, the composition of the reaction gas is changed by thefollowing process corresponding to the quantity of the detected freecarbon. Consequently, the generation of the free carbon can becontrolled.

[0019] (1) Detection of Free Carbon

[0020] a. Change of Reaction Temperature

[0021] The change of a reaction temperature can be used as means forindirectly detecting the generation of free carbon. The reason is asfollows. It is supposed that a temperature in a reactor is generallyuniform when reaction steadily progresses in a fluidized bed reactor.However, deposition of the free carbon which is caused in the reactor isan endothermic reaction. For this reason, a temperature is dropped in aportion where the free carbon is deposited. Therefore, thermometers areinstalled in a portion where the free carbon is easily deposited (aportion closer to the outlet port for product of the reactor) and otherportions in the reactor where the free carbon is deposited withdifficulty, and their measuring temperatures are compared with oneanother. If it is apparent that the temperature in the portion closer tothe outlet port for product is clearly lower than the temperatures inthe other portions, it is possible to decide that the free carbon isdeposited.

[0022] b. Analysis of Dust

[0023] By analyzing dust picked up by means of the dust pick-up device,the free carbon can be directly detected.

[0024] c. Analysis of Gas Composition

[0025] As described above, the free carbon is generated when the ratioof conversion of Fe into Fe₃C has become equal to or greater than aconstant value. In other words, if a ratio of CH₄/H₂ in the gascomposition is raised to a constant value or more as shown by theabove-mentioned reaction formula (4), there is a higher possibility thatthe free carbon might be generated. Accordingly, the gas composition inthe latter half of the compartments of the reactor is analyzed, and thegeneration of the free carbon can be indirectly detected if a value ofCH ₄/H₂ in the above gas has been rapidly reduced.

[0026] d. Combination of Detecting Process

[0027] If two or more of “change of reaction temperature”, “analysis ofdust” and “analysis of gas composition” are combined, the free carboncan be detected more rapidly.

[0028] (2) Change of Reaction Gas Composition

[0029] a. Addition of Steam (H₂O)

[0030] It is not preferable that a ratio of conversion fromiron-containing raw materials into iron carbide be low (equal to orlower than about 90%). The reason is that the grade of the iron carbidehaving the low conversion ratio is too low to be used as raw materialsfor iron making or steel making. On the other hand, if the ratio ofconversion from iron-containing raw materials into iron carbide is toohigh (equal to or higher than about 99%), free carbon is easilydeposited. Therefore, if it is hoped that raw materials for iron makingor steel making with high grade is obtained while controlling thegeneration of the free carbon, it is preferable that the ratio ofconversion from iron-containing raw materials into iron carbide shouldbe kept within a constant range.

[0031] As described above, it is possible to collectively express, bythe following two reaction formula, the reaction where iron carbide(Fe₃C) is produced from iron-containing raw materials using a reactiongas mainly containing hydrogen and methane.

Fe₂O₃+3H₂→2Fe+3H₂O  (5)

3Fe+CH₄→Fe₃C+2H₂  (4)

[0032] In the last stage of the conversion into Fe₃C (in which most ofthe iron-containing raw materials are converted into Fe₃C), the reactionapproaches an equilibrium state. If steam (H₂O) is added into a reactionsystem in the equilibrium state, potentials of hydrogen and oxygen areincreased and potentials of iron and carbon are decreased. Morespecifically, when H₂O is added to the reaction system of the reactionformula (5), a concentration or partial pressure of a molecule on theright side is raised. For this reason, the reaction progresses towardthe left side to recover the equilibrium state. In other words, H₂ isincreased and Fe is decreased. In the reaction formula (4), the reactionprogresses toward the left side in order to consume the increase in H₂and to compensate for the decrease in Fe. As a result, it is possible tocontrol excessive conversion from iron-containing raw materials intoiron carbide.

[0033] Thus, by adding the steam to the reaction gas, the generation ofthe free carbon can be controlled. In addition, it is possible to obtainraw materials for iron making or steel making with high grade in which aratio of conversion into iron carbide is kept within a proper range.

[0034] b. Addition of Carbon Dioxide (CO₂)

[0035] In a case where carbon dioxide is added in place of steam, thefollowing reaction progresses.

CO₂+H₂→CO+H₂O  (6)

[0036] More specifically, addition of CO₂ is synonymous with that ofH₂O. By the above-mentioned action, the generation of free carbon can becontrolled.

[0037] c. Decrease in Quantity of Methane (CH₄) to be Supplied

[0038] A decrease in the quantity of CH₄ to be supplied is equivalent tothe progress of the reaction in the reaction formula (4) toward the leftside or a delay of the progress of the reaction in the reaction formula(4) toward the right side. As a result, excessive conversion fromiron-containing raw materials into iron carbide can be controlled.Consequently, the generation of the free carbon can be controlled. If aquantity of CH₄ to be supplied is excessively reduced, the generation ofthe free carbon can be controlled but a quantity of metallic iron (M—Fe)accumulated in a product is increased. The metallic iron contained inthe product gradually reacts with oxygen in the air at an ordinarytemperature and is then returned to iron oxide. Accordingly, it ispreferable that the quantity of CH₄ to be supplied should not be reducedexcessively but be reduced to obtain such a gas composition to approachan equilibrium state with a solid at that time. Referring to anequilibrium of the gas composition in Fe—CHO reaction system, in otherwords, a concentration of CH₄ is reduced to approach the equilibriumstate in order to correct a carbon potential which is excessively higherthan an equilibrium composition of Fe and Fe₃C. Consequently, thegeneration of the free carbon can be controlled.

[0039] d. Combination of Processes of Changing Reaction Gas Composition

[0040] If two or more of “addition of steam”, “addition of carbondioxide” and “decrease in quantity of methane to be supplied” arecombined, the generation of free carbon can be controlled moreeffectively.

[0041] (3) Process of Changing Reaction Gas Composition

[0042] By controlling a flow rate of a gas to be exhausted from thereactor, a gas composition in the reactor can be changed. However, ifthis process is carried out, a gas balance within the reactor issometimes lost. Therefore, this process is not preferred.

[0043] As compared with the foregoing, a process of increasing a steamcontent of the reaction gas to be introduced into the reactor, addingsteam or carbon dioxide to the reaction gas or decreasing a quantity ofmethane to be supplied can be easily performed directly and has nodrawbacks which are caused by the process of controlling the flow rateof the exhaust gas.

[0044] (4) Other Processes of Controlling Generation of Free Carbon

[0045] Other processes of controlling the generation of free carbon thanthe above-mentioned processes are as follows.

[0046] a. Increase in Quantity of Iron-Containing Material to be Fed andIncrease in Quantity of Iron Carbide to be Discharged

[0047] If the quantity of iron carbide to be discharged is increased,iron carbide in which free carbon is actually deposited is dischargedand iron-containing raw materials having a large number of nonreactedcomponents is increased in the vicinity of the outlet port of thereactor. Once the free carbon is deposited, the generation of the freecarbon is promoted. Therefore, it is preferable that the deposited freecarbon should be discharged quickly. Even if the quantity ofiron-containing raw materials to be fed is increased, the same actioncan be obtained.

[0048] b. Feeding Nonreacted Iron-Containing Raw Materials in Stage inWhich Reducing Reaction and Carburizing Reaction have Progressed toConstant Extent or More

[0049] If nonreacted iron-containing raw materials are fed into aportion in which reducing reaction and carburizing reaction haveprogressed to a constant extent or more and a ratio of conversion intoiron carbide is very high (for example, a portion in the vicinity of theoutlet port of the reactor), oxygen potential is increased in thatportion. Therefore, H₂O is generated and excessive conversion into ironcarbide is inhibited in the same manner as the addition of steam.Consequently, the generation of the free carbon can be controlled.

[0050] c. Drop in Reaction Temperature

[0051] If a temperature is dropped, a reaction speed is reduced so thatthe generation of the free carbon can be controlled.

[0052] (5) Means for Predicting Generation of Free Carbon

[0053] The quantity of metallic iron contained in a product can be usedas means for predicting the generation of free carbon. The reason isthat the ratio of the metallic iron contained in the product is low inthe last stage of the reaction, and iron produced by reducing residualiron oxide immediately is liable to be converted into iron carbide. Morespecifically, very small quantity of metallic iron (or lack of themetallic iron) indicates excessive conversion into iron carbide. If aquantity of the metallic iron contained in the product is known, thegeneration of the free carbon can be predicted. A specific method forpredicting the generation of the free carbon is as follows. A gascomposition in the vicinity of the outlet port of the reactor (which hasan equilibrium relationship with the product) is known by a gaschromatography method, for example, and the quantity of the metalliciron contained in the product is estimated using the gas composition asa basis. Thus, the generation of the free carbon can be predicted.

[0054] According to the present invention described above, the inside ofthe reactor is divided into a plurality of compartments, free carbon isdetected in a latter half of the compartments which are closer to theoutlet port for product, and the composition of a reaction gas ischanged corresponding to the quantity of the detected free carbon. Thus,the generation of the free carbon can precisely be detected and thegeneration of the free carbon can be controlled.

[0055] By employing the above-mentioned process of detecting the freecarbon, the generation of the free carbon can be detected more surely.

[0056] Furthermore, the above-mentioned process is employed to changethe composition of the reaction gas in the reactor. Consequently, thegeneration of the free carbon can be controlled ffectively. Therefore,it is possible to eliminate drawbacks such as blocking of the reactor, adust fire and the like which are caused by the free carbon. In addition,it is possible to produce iron carbide as raw materials for iron makingor steel making with high grade to which no carbon sticks. Furthermore,since the generation of the free carbon can be controlled effectively,it is possible to prevent wasteful consumption of carbon monoxide orhydrocarbon which acts as a resource for producing iron carbide.

BRIEF DESCRIPTION OF DRAWINGS

[0057]FIG. 1 is a schematic diagram showing an example of an apparatusfor producing iron carbide according to the prior art;

[0058]FIG. 2 is a chart representing a transition of each of weightratios of iron carbide (Fe₃C), iron (Fe) and carbon (C) (observed valuesand theoretical values) in a product which is obtained in the case whereiron carbide is produced by reducing and carburizing iron-containing rawmaterials for iron making;

[0059]FIG. 3 is a schematic diagram showing an example of an apparatusfor producing iron carbide according to the present invention;

[0060]FIG. 4 is a schematic diagram showing another example of theapparatus for producing iron carbide according to the present invention;

[0061]FIG. 5 is a schematic diagram showing yet another example of theapparatus for producing iron carbide according to the present invention;

[0062]FIG. 6 is a chart representing a relationship between precent byvolume of H₂O in a fluidized bed reactor and percent by weight of Fe₃Cin a product, which is exerted on the generation of free carbon; and

[0063]FIG. 7 is a chart representing a relationship between percent byvolume of H₂O in a fluidized bed reactor and percent by weight ofmetallic iron (M—Fe) in a product, which is exerted on the generation ofthe free carbon.

BEST MODE FOR CARRYING OUT THE INVENTION

[0064] First of all, a convention method for producing iron carbide willbe described. Next, description will be given to a method forcontrolling the generation of free carbon when producing iron carbide byreducing and carburizing iron-containing raw materials for iron makingaccording to the method of the present invention.

[0065] A. Conventional Method for Producing Iron Carbide

[0066] In accordance with a conventional method, description will begiven to conditions for conversion of iron ore mainly comprisinghematite (Fe₂O₃) into iron carbide (Fe₃C), the schematic structure of areactor and results thereof.

[0067] (1) Condition

[0068] The composition and particle size of iron ore used as rawmaterials, the composition of a reaction gas, a reaction temperature anda reaction pressure are as follows.

[0069] I . Composition of Iron Ore

[0070] 65.3% by weight of Fe, 1.67% by weight of Al₂O₃, 3.02% by weightof SiO₂, 0.080% by weight of P

[0071] II. Particle Size of Iron Ore

[0072] fines having a particle size of 1.0 mm or less (a particle sizeof 0.1 mm to 1.0 mm : 80% by weight or more, a particle size of 0.068 mmor less: 13.4% by weight)

[0073] III. Composition of Reaction Gas (Percent by Volume)

[0074] CH₄:35 to 56%, H₂:33 to 45%, CO: 2.5 to 10%, CO₂:1.2 to 8%,N₂:2.8 to 9.2%, H₂O :0.6 to 1.5%, The total is 100%. IV. Reactiontemperature 590° C. to 650° C. V. Reaction pressure 3 kgf/cm² G(“G”represents a gauge pressure)

[0075] (2) Schematic Structure of Reactor

[0076] As shown in FIG. 1, line 2 for supplying a reaction gas isconnected to a bottom part of fluidized bed reactor 1, and line 3 forexhausting the reaction gas is connected to a top part of the reactor 1.Iron ore is fed into fluidized bed reactor 1 from hopper 4 through line5, and iron carbide product is discharged from line 6.

[0077] (3) Result

[0078] By the above-mentioned conditions, iron carbide was producedusing the reactor shown in FIG. 1. As a result, iron ore was convertedinto iron carbide (Fe₃C) with a transition as shown in FIG. 2. In FIG.2, an ordinate on the left side represents percent by weight of Fe andFe₃C, an ordinate on the right side represents percent by weight of anobserved value and a theoretical value of carbon, and an abscissarepresents a reaction time (hr). As is apparent from FIG. 2, a timetaken for obtaining a ratio of conversion into 93% by weight or more ofiron carbide which is preferable for raw materials for iron making orsteel making was about 6 hours.

[0079] As shown in FIG. 2, while the weight ratio of carbon had atheoretical value of about 6.6% by weight in case of a ratio ofconversion into iron carbide of 100%, an observed value of 8% by weightwas obtained. It is supposed that a difference of “1.4% by weight” wascaused by free carbon.

[0080] B. Method for Producing Iron Carbide According to the PresentInvention

[0081] Description will be given to the schematic structure of a reactorwhich is suitable for carrying out the method of the present inventionand the result of investigations related to effects of reactionconditions which are exerted on the generation of free carbon.

[0082] (1) Schematic Structure of Reactor

[0083] I. Addition of Steam (H₂O) or Carbon Dioxide (CO₂) to ReactionGas

[0084] As shown in FIG. 3, line 7 for supplying H₂O or CO₂ is connectedto a bottom part of fluidized bed reactor 1. An opening of valve 11 isregulated by means of indicator 10 according to a quantity of freecarbon detected by dust meter 9 for detecting free carbon which isinstalled on an upper portion in a latter half of five compartments 8 inthe reactor 1 partitioned by partition wall 8 a that is closer to anoutlet port for product. Thus, a proper quantity of H₂O or CO₂ issupplied into fluidized bed reactor 1. The operation of increasing watercontent in line 2 for supplying the reaction gas is performed by meansof humidifier 18. Alternatively, line 7 is connected to the latter halfof the compartments of the reactor in which free carbon is easilygenerated. Thus, a small quantity of H₂O or CO₂ is supplied to reactor 1through line 7.

[0085] As a result, the generation of the free carbon can be controlledby the above-mentioned mechanism.

[0086] II. Decrease in Quantity of Methane to be Supplied to ReactionGas

[0087] As shown in FIG. 4, line 12 for supplying natural gas isconnected to line 2 for supplying the reaction gas to the bottom part offluidized bed reactor 1. An opening of valve 13 is regulated by means ofindicator 10 according to a quantity of free carbon which is detected bydust meter 9. Thus, a flow rate of the natural gas to be supplied fromline 12 to line 2 is regulated. Natural gas is a lower paraffin basedhydrocarbon (C_(n)H_(2n+2)) containing methane as a main component andnecessary for carburizing reaction. In order to promote thecarburization, the natural gas is added to the reaction gas in line 2 ifnecessary. If the free carbon is generated in fluidized bed reactor 1,the opening of valve 13 is regulated to reduce the quantity of thenatural gas to be supplied into reactor 1. Thus, the generation of thefree carbon is controlled. In this case, a line (not shown) forsupplying hydrogen may be connected to line 2, and hydrogen may besupplied from the hydrogen supply line to line 2 according to thequantity of the free carbon which has been detected by dust meter 9.Thus, a concentration of methane contained in the reaction gas isrelatively reduced. Consequently, the generation of the free carbon canbe controlled.

[0088] In place of the above-mentioned dust meter 9, a gas pick-updevice may be installed. A ratio of methane to hydrogen in the gaspicked up by the gas pick-up device may be detected by a gaschromatography method or the like. If the ratio of methane has beenrapidly reduced, the generation of the free carbon can be predicted.

[0089] III. Drop in Reaction Temperature in Fluidized Bed Reactor

[0090] If a reaction temperature is dropped, a reaction speed isrelatively reduced so that the generation of free carbon can becontrolled. For example, as shown in FIG. 5, thermometers 14, 15 and 16are inserted into the compartments in the vicinity of an inlet port foriron ore, a central portion and the vicinity of an outlet port forproduct of fluidized bed reactor 1, respectively. Thus, the temperaturesare monitored by means of instrument 17. In a case where a reaction influidized bed reactor 1 progresses in a steady state, the temperaturesmeasured by the thermometers 14, 15 and 16 are almost equal to oneanother. However, in a case where free carbon has been generated inreactor 1, the temperature in that portion is lower than thetemperatures in other portions because the generation of the free carbonis endothermic reaction. In general, iron ore has a high ratio ofconversion into iron carbide in the vicinity of the outlet port forproduct. In this portion, free carbon is easily generated. By comparingthe temperature measured by thermometer 16 with the temperatures inother portions, the generation of the free carbon can be indirectlyknown. For example, if a temperature T₀ measured by thermometer 16 islower than each of temperatures T_(1a) and T_(2a) measured bythermometers 14 and 15 by a temperature of 30 to 50° C., it is supposedthat the free carbon has been generated. If the operation is carried outin such a manner that each of temperatures T_(1b) and T_(2b) measured bythermometers 14 and 15 is lower than each of the temperatures T_(1a) andT_(2a) in order to make a conversion ratio into iron carbide less thanthe conversion ratio based on the conditions in fluidized bed reactor 1(the temperatures T_(1a), T_(2a) T₀ and the ratio of conversion intoiron carbide) at that time, the generation of free carbon can becontrolled.

[0091] (2) Effect of Reaction Condition Exerted on Generation of FreeCarbon

[0092] I. Effect of Steam (H₂O)

[0093]FIG. 6 is a chart representing the effect of percent by volume ofH₂O which is exerted on the generation of free carbon in the case whereiron ore having the above-mentioned composition and particle size hasbeen converted into iron carbide (Fe₃C) using a reaction gas having theabove-mentioned composition at a temperature of 590 to 650° C. and apressure of 3 to 4 kgf/cm² G in the fluidized bed reactor 1. In FIG. 6,mark ‘◯’ indicates a case where the free carbon has been not generated,and mark ‘▴’ indicates a case where the free carbon has been generated.As is apparent from FIG. 6, if percent by volume of H₂O is increased, aregion where the free carbon is not generated (a right region of a lineconnecting marks ‘◯’ in FIG. 6 is the region where the free carbon isnot generated) is increased. More specifically, if steam is added, thefree carbon is generated with difficulty even if the ratio of conversioninto the iron carbide has been increased.

[0094] II. Influence of Metallic Iron

[0095]FIG. 7 is a chart representing a relationship among metallic iron(M—Fe) in a product, percent by volume of H₂O and the status ofgeneration of free carbon, in the case where iron ore having theabove-mentioned composition and particle size has been converted intoiron carbide (Fe₃C) using a reaction gas having the above-mentionedcomposition at a temperature of 590 to 650° C. and a pressure of 3 to 4kgf/cm² G in fluidized bed reactor 1. In FIG. 7, mark ‘◯’ and mark ‘▴’have the same meanings as in FIG. 6. As is apparent from FIG. 7, if theratio of metallic iron (M—Fe) is reduced with the same percent by volumeof H₂O, the free carbon is easily generated. The reason is that theratio of the metallic iron contained in the product is very small in thelast stage of the reaction and metallic iron obtained by reducingresidual iron oxide in the iron ore immediately easily tends to beconverted into iron carbide. Thus, the ratio of conversion into ironcarbide is excessive in the last stage of the reaction. As a result, thefree carbon is easily generated. Thus, lack of the metallic iron causesthe generation of the free carbon. Therefore, if the quantity of themetallic iron contained in the product can be obtained by analyzing thecomponent of the product, the generation of the free carbon can bepredicted. A gas in the vicinity of the outlet port of the fluidized bedreactor has an equilibrium relationship with a product (raw material foriron making and steel making mainly comprising iron carbide) to bedischarged from the outlet port. Therefore, a gas composition in thevicinity of the outlet port is detected by a gas chromatography method,for example, thereby estimating the quantity of the metallic ironcontained in the product. Thus, the generation of the free carbon can bepredicted and a precise countermeasure for controlling the generation ofthe free carbon can be taken.

INDUSTRIAL APPLICABILITY

[0096] Since the present invention has the above-mentioned constitution,the apparatus according to the present invention is suitable for anapparatus for producing iron carbide in which free carbon is generatedwith difficulty.

1. (cancelled)
 2. (amended) A method for producing iron carbide in whichfree carbon can be prevented from being generated by thermaldecomposition of carbon monoxide or hydrocarbon when raw materials foriron making or steel making mainly comprising iron carbide as a maincomponent is produced by reducing and carburizing iron-containing rawmaterials for iron making mainly comprising iron oxides and ironhydroxides as main components using a reaction gas mainly containinghydrogen and methane, comprising the steps of dividing an inside of areactor into a plurality of compartments, detecting the free carbonaccording to a change of a temperature of a thermometer installed in alatter half of the compartments which are closer to an outlet port forproduct, and changing a composition of the reaction gas corresponding toa quantity of the detected free carbon.
 3. (cancelled)
 4. (amended) Themethod for producing iron carbide of claim 2 , wherein the free carbonis detected according to a result of detection of a ratio of methane tohydrogen in gas picked up by a gas pick-up device installed on an upperportion in the latter half of the compartments.
 5. (amended) The methodfor producing iron carbide of claim 2 , wherein the free carbon isdetected by combining two or more of a process of detecting the freecarbon according to a change of a temperature of a thermometer installedin the latter half of the compartments, a process of detecting the freecarbon by analyzing dust picked up by a dust pick-up device installed onan upper portion in the latter half of the compartments and a process ofdetecting the free carbon according to a result of detection of a ratioof methane to hydrogen in gas picked up by a gas pick-up deviceinstalled on the upper portion in the latter half of the compartments.6. (cancelled)
 7. (amended) The method for producing iron carbide ofclaim 2 , wherein the composition of the reaction gas in the reactor ischanged by increasing carbon dioxide in the reaction gas correspondingto the quantity of the detected free carbon.
 8. (cancelled) 9.(cancelled)
 10. (amended) The method for producing iron carbide of claim7 , wherein the composition of the reaction gas in the reactor ischanged by controlling the composition of the reaction gas to beintroduced into the reactor.
 11. (added) A method for producing ironcarbide in which free carbon can be prevented from being generated bythermal decomposition of carbon monoxide or hydrocarbon when rawmaterials for iron making or steel making mainly comprising iron carbideas a main component is produced by reducing and carburizingiron-containing raw materials for iron making mainly comprising ironoxides and iron hydroxides as main components using a reaction gasmainly containing hydrogen and methane, comprising the steps of dividingan inside of a reactor into a plurality of compartments, detecting thefree carbon in a latter half of the compartments which are closer to anoutlet port for product, and increasing the quantity of iron carbideproduct to be discharged corresponding to a quantity of the detectedfree carbon.
 12. (added) The method for producing iron carbide of claim11 , wherein nonreacted iron-containing raw materials are fed into alatter half of the compartments in place of increase in quantity of ironcarbide product to be discharged.
 13. (added) A method for producingiron carbide in which free carbon can be prevented from being generatedby thermal decomposition of carbon monoxide or hydrocarbon when rawmaterials for iron making or steel making mainly comprising iron carbideas a main component is produced by reducing and carburizingiron-containing raw materials for iron making mainly comprising ironoxides and iron hydroxides as main components using a reaction gasmainly containing hydrogen and methane, comprising the steps ofmeasuring a quantity of metallic iron contained in iron carbide product,and changing a composition of the reaction gas in the reactorcorresponding to the quantity of the metallic iron.